Directions: 1. Prepare the potatoes: Have ready the 8-quart kettle with 4 cups of cold water. Peel the potatoes and slice them 1/4 inch thick, putting them into the cold water to cover as you prepare the remaining potatoes. Cover the kettle and bring to a boil. Uncover and boil slowly for 3 to 4 minutes until barely cooked through. Drain and let stand covered for 3 to 4 minutes to in order to firm up the potato slices, then uncover.

2. Make the garlic and mustard sauce: Melt butter in a saucepan, then blend in the flour with a wooden spoon to make a smooth paste. Cook together until they foam and froth for 2 minutes without browning. Off the heat, pour in half of the hot milk and whisk vigorously. Continue to whisk to blend as you pour in the remainder of the milk. Then whisk slowly over moderately high heat, scraping bottom and sides of the pan, until the sauce comes to the simmer. Simmer 2 to 3 minutes. Remove from heat and whisk in the seasonings. Bring to the simmer again, tasting and add additional seasonings if needed.

3. Assembling: Spoon a 1/16-inch layer of sauce into the bottom of the buttered baking dish. Set 3 cups of the sauce and 1 cup of the cheese aside for the topping. To arrange everything in 4 layers, start with a quarter of the potatoes, then a quarter of the ham, then a third of the sauce, and last a third of the cheese. Continue in layers, finishing the final layer with the remaining potatoes and ham. Spread on the reserved 3 cups of sauce to cover completely, then the last of the cheese.

4. Final Baking: Preheat oven to 375 degree an hour or so before you plan to serve. Bake in the upper third of the oven until the potatoes are bubbling hot and the top had browned nicely.